Live birth of a bear cub following nonsurgical embryo collection

In the near future, 6 of 8 bear species will face extinction mainly because of loss of their natural habitat. This loss of habitat will ultimately require some of these bears to be maintained in zoos and wildlife preserves in the hope of conserving genetic diversity. If the giant panda is representative of other bear species, reproductive performance will be inhibited in such an environment. In this study, we used the nonendangered American black bear (Ursus americanus) as the model for developing appropriate embryo transfer procedures. The donor bear mated numerous times between late May and early June. In late July we anesthetized her and used a series of telescoping sheaths to gain access to the uterus Then we passed a catheter through the largest sheath, inflated the balloon, and, using a 20-mL syringe, repeatedly infused into and then aspirated from the uterus PBS + BSA. We emptied the syringe into Petri dishes and observed 2 embryos. We rinsed the embryos, placed them in human tubal fluid + HSA + HEPES and then held them at 35 degrees C for 5 h. The recipient mated during mid-June; in late July we anesthetized her and, with the aid of laparoscopy, transferred an embryo into the cranial portion of the uterine horn ipsilateral to the ovary containing a CL. The recipient delivered 2 cubs in January. Necropsy results indicated that the neonates lived for 6 to 8 wk before succumbing to flooding in the den. The DNA from hair samples belonging to the neonates indicated that the male cub belonged to the donor, the female cub to the recipient. The delayed implantation mechanism in bears probably allowed for the successful development of the embryo in the presence of a substantial asynchrony between the donor and the recipient (13 d). We conclude that embryo transfer is possible in the American black bear and can lead to the birth of live cubs.